w = linspace(-pi, pi, 1000);

z = exp(j*w);

H = ((1 - 1.5.*z.^-1 - z.^-2).*(1 + 0.9.*z.^-1)) ./ ((1 - z.^-1) .* (1 + 0.7.*j.*z.^-1) .* (1 - 0.7.*j.*z.^-1));
plot(w, abs(H))
axis([-pi pi -3 30])
title('|H^{ej\omega}|')
xlabel('\omega')
